The origin of fluids involved in the formation of gold-bearing skarns of the Andorra granite (Central Pyrenees,Spain): Sulphur isotope data

Summary Arsenopyrite-gold mineralization in the lower Paleozoic series of the eastern Pyrenees is of two types: disseminated in Hercynian metasediments, and veins cross-cutting the main foliation. In the central Pyrenees, gold-bearing arsenopyrite mineralizations have recently been discovered in skarns along the SW contact of the Andorra granite. The ore minerals are similar to those of the veins, with gold also being associated with arsenopyrite, bismuth and sulphides.The late Hercynian Andorra granite intruded Paleozoic metasediments of pre-Caradocian to Carboniferous age. Six types of skarns have developed at or close to the contact between the granite and Devonian limestones. Only three of these, the hedenbergite, pyrrhotite and arsenopyrite skarns, are sulphide-bearing. Gold grades in these skarns range from less than 0.8 g/t in pyrrhotite skarns to 7 g/t in arsenopyrite skarns.The ³⁴S of arsenopyrite from disseminated and vein mineralizations show values from 11 to 15, indicating a sulphur source of crustal origin. Vein sulphides are considered to have formed after a metamorphic remobilization of the sulphide rich disseminations in the Paleozoic series. Sulphur isotopic composition of skarn sulphides is variable: pyrrhotite from pyrrhotite skarns has a ³⁴S +, suggesting a sulphur of magmatic origin. Their gold grades are very low (>0.8 g/t). The heavier values of arsenopyrite from arsenopyrite skarns (³⁴S + 10) and of galena and sphalerite from hedenbergite skarns (³⁴S + 7) correlate with the higher gold grades (7 and 5 g/t, respectively). This is interpreted to reflect a contribution of wall-rock sulphur-rich fluids generated from the thermal metamorphism of arsenopyrite-bearing wall-rock metasediments (³⁴S + 12%o) during skarn formation or by assimilation of country rock by the granitic intrusion during its emplacement. The economic importance of these skarns appears to be related to the amount of crustal fluid involved in skarn formation.

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Lagerstättenbildende Fluide in den goldführenden Skarnen des Andorra-Granites, Zentralpyrenäen, Spanien: Schwefelisotopen-Daten

Zusammenfassung Arsenkies-Goldmineralisation in altpaläozoischen Serien der ostlichen Pyrenäen tritt in zwei Typen auf: Disseminiert in Hercynischen Metasedimenten, und in Gängen, die die Haupt-Foliation durchschlagen. In den Zentralpyrenäen wurden goldführende Arsenkies-Mineralisationen vor kurzem in Skarnen längs des SW-Kontaktes des Andorra-Granites entdeckt. Die Erzminerale sind ähnlich denen in den Gängen, wobei Gold mit Arsenkies, Wismut und Sulfiden assoziiert ist. Der spät-hercynische Andorra-Granit intrudierte paläozoische Metasedimente von Prä-Caradoc bis Karbon-Alter. Im Kontaktbereich Granit/Devonische Kalke kommen sechs Typen von Skarnen vor. Nur drei davon führen Sulflde, nämlich die Hedenbergit-, Magnetkies- und Arsenkiesskarne. Goldgehalte in diesen Skarnen schwanken von weniger als 0,8 g/t in Magnetkiesskarnen bis zu 7 g/t in Arsenkiesskarnen. Das ö34 S von Arsenopyrit in disseminierten und Gang-Mineralisationen schwankt von 11-15%o, und dies weist auf eine Schwefelquelle in der Kruste hin. Gangsulflde haben sich auch nach einer metamorphen Remobilisierung der Sulfid-reichen Disseminationen in den paläozoischen Serien gebildet. Die Schwefelisotopenzusammensetzung der Skarnsulfide schwankt: Magnetkies aus Magnetkiesskarnen hat ö34 S Werte von +4%o, dies weist auf magmatischen Ursprung hin. Ihre Goldgehalte sind sehr niedrig (<0,8 0,8 g/t). Die schwereren Isotopen von Arsenkies in Arsenkies-Skarnen ( ³⁴S+ 10%o) und von Bleiglanz und Zinkblende aus den Hedenbergit-Skarnen ( ³⁴S+ 7%o) lassen sich mit höheren Goldgehalten (7 und 5 g/t) korrelieren. Dies wird Fluiden zugeschrieben, die reich an Schwefel aus den Nebengesteinen sind und durch die thermale Metamorphose der Arsenkies-führenden Metasedimente (S + 12%o) während der Skarnbildung, oder durch Assimilation von Nebengestein durch den Granit wahrend seiner Platznahme entstanden sind. Die wirtschaftliche Bedeutung dieser Skarne scheint in einer direkten Beziehung zur Menge krustaler Fluide zu stehen.

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This paper was presented at the IGCP 291 Project Symposium Metamorphic Fluids und Mineral Deposits, ETH Zürich, March 21–23, 1991.     

Habitat changes in coastal wetlands associated to hydrological changes in the watershed

In recent decades wetlands associated with the Mar Menor lagoon (SE Spain) have undergone several hydrological and biological changes as a consequence of increased water inputs from agricultural drainage off the watershed. Changes in the vegetal communities were studied by means of supervised classification of Landsat images, and TM and ETM+ sensors during the period 1984–2000, and a series of land cover maps was created. Changes in the wetland area during this period were analysed and a good fit was found with the total area of irrigated lands in the watershed. The series of land cover maps also allowed the study of the internal composition of the vegetal communities in each wetland. Important changes were detected, with an expansion of reedbeds and a significant reduction in the area occupied by priority habitats according to the Habitats Directive.     

‘This is my garden’: justice claims and struggles over forests in Vietnam’s REDD+

ABSTRACT

This paper explores dynamics of conflict over forests in Vietnam, as the country lays the groundwork for Reducing Emissions from Deforestation and Forest Degradation (REDD+). Drawing on a case study in Lam Dong province and applying an environmental justice lens, we examine how various social actors assert claims over forests and how these claims invoke different notions of justice, authority and identity. Our analysis highlights that the development and implementation of the project has generated renewed competing claims and conflicts over forests among social actors. Underlying these conflicts there are incompatible notions of justice and associated rights, which lead different actors to accord legitimacy variously to the global norms brought about by REDD+, the customary resource practices of indigenous people, or to the state’s laws. We show that the negotiations over forests in REDD+ reflect the influence of the specific historical and political-economic settings in which REDD+ activities take place, including pre-existing conflicts over forests and power relations underpinning forest management. From a policy perspective, our research suggests that any attempts to introduce simplified and uniform regulations for forest governance in REDD+ should be avoided, since local institutions and conceptions of justice will significantly influence what is regarded as legitimate policy and can thus be endorsed as inspiration for sustainable forest governance.

Key policy insights

• REDD+ in Vietnam has spurred contestations over who is legitimately entitled to govern and manage forests.

• Claims and conflicts over forests can be explained by incompatible and distinct notions of justice, authority and identity.

• Contestations over justice pose radical challenges to any global and national efforts that attempt to implement simplified rules and ideas for forest based-climate change mitigation.

• Attention to justice, especially to compatibility and differences in ideas about justice, is crucial for sustainable forest governance.

     

Equity implications of marketing ecosystem services in protected areas and rural communities: Case studies from Meso-America

This paper investigates the equity implications of marketing ecosystem services in protected areas and rural communities. We use a three-tiered equity framework to analyse four distinct efforts to commercialise watershed recharge and carbon dioxide fixation by forests in Meso-America. We show that project development and participation are strongly mediated by organisational networks, as well as existing rights of access over land and forest resources. We demonstrate that procedural fairness diverges strongly when initiatives are implemented in protected areas or in rural communities. While in the former reserve managers and intermediaries concentrate all decision-making power, initiatives working with rural communities are able to integrate more significantly service providers in management decisions. Marketing ecosystem services in protected areas contributes to reduce expenditure rates for protected area management, but also results in less equitable outcomes, as rural communities and forest resource users become excluded from receiving sustained development benefits. When ecosystem services are commercialised by rural farmers, payments do not cover opportunity costs but act as a significant incentive for participation in most cases. Ecosystem service providers also benefit from complementary project activities, such as forest management training and agricultural extension support. We argue that limited economic impact and existing inequities in decision-making and outcomes can be explained by problems of institutional design, in particular the inability of markets and payments for ecosystem services to account for context-related factors, such as property rights.     

Associations between outdoor air quality and birth weight: a geostatistical sequential simulation approach in Coastal Alentejo,Portugal

Several environmental health studies suggest birth weight is associated with outdoor air pollution during gestation. In these studies, exposure assignments are usually based on measurements collected at air quality monitoring stations that do not coincide with health data locations. So, estimated exposures can be misleading if they do not take into account the uncertainty of exposure estimates. In this article we conducted a semi-ecological study to analyze associations between air quality during gestation and birth weight. Air quality during gestation was measured using a biomonitor, as an alternative to traditional air quality monitoring stations data, in order to increase spatial resolution of exposure measurements. To our knowledge this is the first time that the association between air quality and birth weight is studied using biomonitors. To address exposure uncertainty at health locations, we applied geostatistical simulation on biomonitoring data that provided multiple equally probable realizations of biomonitoring data, with reproduction of observed histogram and spatial covariance while matching for conditioning data. Each simulation represented a measure of exposure at each location. The set of simulations provided a measure of exposure uncertainty at each location. To incorporate uncertainty in our analysis we used generalized linear models, fitted simulation outputs and health data on birth weights and assessed statistical significance of exposure parameter using non-parametric bootstrap techniques. We found a positive association between air quality and birth weight. However, this association was not statistically significant. We also found a modest but significant association between air quality and birth weight among babies exposed to gestational tobacco smoke.     

Caractérisation géochimique des fluides associés aux minéralisations PbZn de Bou-Dahar (Maroc)

The Bou-Dahar PbZn Mississippi Valley deposits located in the eastern part of the High Atlas Range (Morocco) are hosted by a Liassic reefal complex. Fluid inclusion and ‘crush-leach’ data show that two distinct fluids were involved in the mineralisation deposition: a warmer, more saline fluid (180?°C, $>25\text{wt\%}$ NaCl equivalent) and a cooler, less saline fluid (70?°C, 16 wt% equivalent NaCl). Mixing of these two fluids resulted in the precipitation of the ore. The solute composition of the ore-forming brine suggests that the MVT mineralising fluids were probably a mixture of halite-dissolution fluids and evaporated seawater. To cite this article: S. Adil et al., C. R. Geoscience 336 (2004).     

Mineralisation from Vall de Ribes area (Eastern Pyrenees,Spain)

Vein mineralisation with no preferred orientation, cutting lower Palaeozoic rocks, and local replacement deposits in dolomite show a zoning in tungsten-bismuth, arsenic and antimony minerals away from the adjacent late-Hercynian Costabona granite. A local reversed zoning is related to higher temperatures indicated by fluid inclusion study. Many of the minerals have not previously been reported from this area.     

Free advanced modeling and remote-sensing techniques for wetland watershed delineation and monitoring

Watershed scale studies focusing on hydrological pressures influencing freshwater ecosystem dynamics are necessary for the establishment of suitable wetland ecological indicators. Enhanced and reproducible methods for watershed modeling and land-cover assessment are thus essential tools for wetland monitoring and management. However, few integrated studies propose advanced open source methodologies for watershed modeling and assessment. In this study, a set of GIS methodological tools was applied and further developed in order to delineate wetland watersheds and map their land-cover changes over time. Watersheds draining to 11 semiarid Mediterranean saline wetlands were delimited and map algebra operations were applied on the digital elevation model in the Campo de Cartagena coastal plain to enhance watershed delimitation. land-use/land-cover maps of wetland watersheds were obtained for years 1987 and 2008 by means of supervised classification of Landsat images. A set of four spectral indices was included in the classification analysis using a combination of bands in order to improve the discrimination of vegetation, water bodies, infrastructure, and bare soil. An iterative classification procedure based on maximum likelihood and random selection of training areas was applied. Contextual information based on automatic image segmentation of Landsat scenes was also included as ancillary layers. Watershed areas obtained ranged from 70 to 17,000 ha and delineation was improved in the Campo de Cartagena coastal plain. The proposed image classification methodology showed high accuracies and improved standard classification techniques. The proposed methodology is based on free and open source tools, which makes it broadly applicable.